The most common system for retaining the sealing ring in the socket portion of the joints is the use of a sealing ring groove which is defined in the inner portion thereof. In addition to a simple inwardly facing ring groove for retaining such sealing rings, a number of systems have been developed to more fixedly retain this sealing ring in the desired position.
U.S. Pat. No. 3,924,999, assigned to the assignee of the present invention, locks the sealing ring within the groove by thermoplastically deforming the lateral walls of the ring groove at spaced locations with the use of deforming members. These deforming members move at oblique angles to the sealing ring while the sealing ring is positioned on a mandrel assembly. The thus formed sealing ring groove incorporates a plurality of spaced segments which grip the enlarged outer portion of the sealing ring, thus preventing its displacement.
In U.S. Pat. No. 3,520,047 a sealing ring is held in place in the ring groove by the use of one or a pair of supporting rings flanking the sealing ring. These supporting rings are substantially rigid and define there between an annular space which firmly holds the sealing ring in place. Also, this patent states that the sealing ring and the support ring or rings may be firmly connected together by, for example, molding the sealing ring to the support ring. The support ring also serves as an annular ramp for radially expanding the heat-softened leading edge of a thermoplastic pipe over the sealing ring.
U.S. Pat. No. 3,836,622 shows three pipe joint arrangements. The first shows a sealing ring having a cross sectional configuration in which the axial dimension of the outer diameter exceeds inner diameter. The sealing ring is initially positioned within the profile of a forming mandrel while a heat-softened portion of thermoplastic pipe is led over this mandrel. The sealing ring is radially expanded to its approximate final configuration which further expands the heat-softened pipe and begins to form the sealing ring groove. Finally, annular jaws force the lateral wall portions of the ring groove inwardly to clampingly retain the sealing groove in its radially expanded position and aid in holding the sealing ring in this sealing position during assembly and use of the pipe joint.
A second configuration employs the use of a sealing ring having a circular cross section (a classic O-ring) which is rolled from a notched position in the forming mandrel by the leading edge of the heat-softened thermoplastic pipe. This action positions the O-ring in a ring groove as well as expands the O-ring to its approximate final dimension. Finally, clamping jaws conform the wall of the thermoplastic pipe to the outer surface of the O-ring.
A third pipe joint configuration includes a socket which is formed of a thermosetting plastic cast around a sealing ring having an outer, wedge-shaped portion. The thermosetting plastic is formed around at least this outer portion, thus locking the sealing gasket in its final, operative position.
As illustrated by the above cited patents, there exist systems for forming the pipe joint, and in particular for forming the ring groove about a pre-positioned sealing ring.
U.S. Pat. No. 3,793,427, assigned to the assignee of the present invention, demonstrates the use of a series of ramp bars pivotally attached to the forward portion of the mandrel. These bars can be positioned so as to cause the heat-softened pipe to expand beyond the outer diameter of the sealing ring, and then be pivoted inwardly to a position such that the heat-softened pipe collapses inwardly to form a substantially cylindrical portion of the socket. In this way, a retainer ring, such as that disclosed in U.S. Pat. No. 3,520,047, need not be used to lead the pipe over the sealing ring.
U.S. Pat. No. 3,484,900 shows a different system for forming the ring groove. In this system, an elastomeric, radially expandable section of the forming mandrel is caused to move radially outward by an axially moving conical cam surface. This radial outward expansion forces a section of heat-softened pipe to move outwardly in conformity to a female mold. On cooling, the resulting pipe section has a square-shouldered ring groove defined therein. The expansible elastomeric portion is permitted to move radially inwardly to permit the thus cooled socket to be removed from the mandrel.
Another similar use of an elastic or elastomeric expandable mandrel section is shown in U.S. Pat. No. 3,998,578.